Add DemoRunner.java

src/main/java/com/ankurm/sdjpa4demo/DemoRunner.java

@@ -0,0 +1,112 @@
+package com.ankurm.sdjpa4demo;
+
+import com.ankurm.sdjpa4demo.domain.Author;
+import com.ankurm.sdjpa4demo.domain.Book;
+import com.ankurm.sdjpa4demo.repo.AuthorRepository;
+import com.ankurm.sdjpa4demo.repo.BookRepository;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.dao.EmptyResultDataAccessException;
+import org.springframework.dao.IncorrectResultSizeDataAccessException;
+import org.springframework.data.domain.Sort;
+import org.springframework.context.annotation.Profile;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.math.BigDecimal;
+import java.util.List;
+import java.util.Optional;
+
+@Component
+@Profile("!test")
+public class DemoRunner implements CommandLineRunner {
+
+    private final AuthorRepository authors;
+    private final BookRepository books;
+
+    public DemoRunner(AuthorRepository authors, BookRepository books) {
+        this.authors = authors;
+        this.books = books;
+    }
+
+    private static void section(String title) {
+        System.out.println("\n================ " + title + " ================");
+    }
+
+    @Override
+    @Transactional
+    public void run(String... args) {
+        Author gof   = authors.save(new Author("Erich Gamma", "CH"));
+        Author bloch = authors.save(new Author("Joshua Bloch", "US"));
+        Author anon  = authors.save(new Author("Anonymous", null));   // null country
+        authors.save(new Author("Martin Fowler", "UK"));
+        authors.save(new Author("Kent Beck", "DE")); // bookless: safe to delete in section G
+
+        books.save(new Book("Design Patterns", new BigDecimal("42.00"), gof));
+        books.save(new Book("Effective Java", new BigDecimal("45.00"), bloch));
+        books.save(new Book("Refactoring", new BigDecimal("45.00"), anon)); // duplicate price 45.00
+
+        // (A) Optional vs non-null vs @Nullable single-result semantics
+        section("A. Null-handling of single-result query methods");
+        Optional<Author> opt = authors.findByName("No Such Author");
+        System.out.println("findByName(Optional) missing -> " + opt);
+
+        try {
+            authors.getByName("No Such Author");
+        } catch (EmptyResultDataAccessException ex) {
+            System.out.println("getByName(non-null) missing -> throws " + ex.getClass().getSimpleName());
+        }
+
+        Author byCountry = authors.findByCountry("ZZ");
+        System.out.println("findByCountry(@Nullable) missing -> " + byCountry);
+
+        // (B) JSpecify @NullMarked rejects null arguments at runtime
+        section("B. JSpecify @NullMarked parameter enforcement");
+        try {
+            authors.getByName(null);
+        } catch (IllegalArgumentException ex) {
+            System.out.println("getByName(null) -> throws " + ex.getClass().getSimpleName()
+                    + ": " + ex.getMessage());
+        }
+        System.out.println("findByCountry(null) is allowed (@Nullable param) -> "
+                + authors.findByCountry(null));
+
+        // (C) NULLS precedence in Sort (consistent in SD JPA 4)
+        section("C. NULLS FIRST vs NULLS LAST in Sort");
+        List<Author> nullsFirst = authors.findByNameStartingWith(
+                "", Sort.by(Sort.Order.asc("country").nullsFirst()));
+        System.out.println("country ASC NULLS FIRST -> "
+                + nullsFirst.stream().map(Author::getCountry).toList());
+        List<Author> nullsLast = authors.findByNameStartingWith(
+                "", Sort.by(Sort.Order.asc("country").nullsLast()));
+        System.out.println("country ASC NULLS LAST  -> "
+                + nullsLast.stream().map(Author::getCountry).toList());
+
+        // (D) Derived query now flows through JPQL (see generated SQL just above in log)
+        section("D. Derived query -> JPQL path");
+        System.out.println("findByNameStartingWith('J') -> "
+                + authors.findByNameStartingWithOrderByNameAsc("J")
+                        .stream().map(Author::getName).toList());
+
+        // (E) New JPA 3.2 JPQL: || concatenation + replace()
+        section("E. New JPQL functions ( || and replace() )");
+        System.out.println("badgeFor(gof)  -> " + authors.badgeFor(gof.getId()));
+        System.out.println("badgeFor(anon) -> " + authors.badgeFor(anon.getId()));
+
+        // (F) Single-result that matches multiple rows -> non-unique edge case
+        section("F. Non-unique single result edge case");
+        try {
+            Book b = books.findByPrice(new BigDecimal("45.00"));
+            System.out.println("findByPrice(45.00) -> " + b);
+        } catch (IncorrectResultSizeDataAccessException ex) {
+            System.out.println("findByPrice(45.00) matches 2 rows -> throws "
+                    + ex.getClass().getSimpleName());
+        }
+
+        // (G) Derived DELETE returns affected count
+        section("G. Derived delete returns count");
+        long deleted = authors.deleteByCountry("DE");
+        System.out.println("deleteByCountry('DE') removed -> " + deleted + " row(s)");
+
+        section("DONE");
+    }
+}